Re: 1 week old. overfeeding?reflux? gas?

If there isn't any pain and everything else seems fine, then I woudn't worry about it. My baby spit up huge amounts constantly when he was a newborn. I had a receiving blanket draped over me at all times back then, because a burp cloth wasn't even close to being large enough to protect me from the spewing. It wasn't fun, but it was perfectly normal. Keeping your baby upright for awhile after feedings can help a little, but for us there was still copious amounts of spit up.

Re: 1 week old. overfeeding?reflux? gas?

When baby is growing normally and is not in pain when spitting up, spit-up is a laundry problem, not a health problem. The amounts may appear quite large, but generally are not as big as moms think. To get a sense of how much is really coming back up, pour an oz of milk (cow's milk, please!) on the counter. You'll probably realize that a small amount of milk looks like quite a bit more when it's spilled everywhere. The appearance of the milk itself changes based on how long it has been in baby's tummy. If the baby has just nursed, the spit-up will appear thin and milky. If it has been a while since baby last fed, the spit-up will appear chunky or cheesy.

Spit-up and fussiness/gassiness have very little relation to each other. Don't worry that you're somehow causing or failing to prevent these very normal baby issues. They are pretty much beyond your control.